Beginner tips for a Back-End Developer

Hey. I’ve already posted a topic on front-end development and newbie tips on that but what should I do, if I want to be a back-end developer? I looked at the Learning Paths and saw that Mosh has 3 courses before learning other languages. Would I first learn these topics and then choose a language? Or do I do all the languages?

tldr: What do jobs look for in a candidate-> Does that translate to one language or multiple? Do I first learn the 3 courses before a language?

(sorry if this topic seems dumb, im a complete newbie and although im only a junior in hs, im completely stressing over the fact that i need to be presentable to colleges and jobs in the future)